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Debt - Narrative (Details) |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
May 14, 2021 | Apr. 14, 2021 USD ($) | Apr. 09, 2021 USD ($) $ / shares | Apr. 07, 2021 USD ($) $ / shares | Apr. 29, 2019 USD ($) payment | Apr. 30, 2021 USD ($) | Jun. 30, 2021 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) | Jun. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  |  |  |  |  |  |  | $ 250,000,000.0 | $ 0 |
Loss on early extinguishment of debt |  |  |  |  |  |  | $ (24,700,000) | $ 0 | (24,700,000) | 0 |
Proceeds from convertible notes |  |  |  |  |  |  |  |  | $ 86,300,000 | $ 0 |
Senior notes [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loss on early extinguishment of debt |  |  |  |  |  | $ 24,700,000 |  |  |  |  |
Redemption premium |  |  |  |  |  | 18,100,000 |  |  |  |  |
Write off of deferred financing cost |  |  |  |  |  | 4,400,000 |  |  |  |  |
Debt discount |  |  |  |  |  | 2,200,000 |  |  |  |  |
Senior secured notes, 7.5% [Member] | Senior notes [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate, percentage |  | 7.50% |  |  |  |  | 7.50% |  | 7.50% |  |
Face amount |  | $ 250,000,000.0 |  |  |  |  |  |  |  |  |
Proceeds from issuance of debt |  | $ 245,200,000 |  |  |  |  |  |  |  |  |
Redemption price, percentage |  |  |  |  |  |  |  |  | 100.00% |  |
Redemption period |  |  |  |  |  |  |  |  | 12 months |  |
Percentage of outstanding amount, offer to purchase |  |  |  |  |  |  | 101.00% |  | 101.00% |  |
Senior secured notes, 7.5% [Member] | Senior notes [Member] | Level 2 [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fair value of debt instrument |  |  |  |  |  |  | $ 265,400,000 |  | $ 265,400,000 |  |
Senior secured notes, 12.0% [Member] | Senior notes [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate, percentage |  |  |  |  |  |  | 12.00% |  | 12.00% |  |
Redemption price, percentage | 107.00% |  |  |  |  |  |  |  |  |  |
Debt instrument, repurchased face amount |  |  |  |  |  | $ 195,900,000 |  |  |  |  |
Debt discount |  |  |  |  |  |  | $ 2,300,000 |  | $ 2,300,000 |  |
Convertible senior note [Member] | Call Option [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Issuance cost |  |  |  | $ 5,700,000 |  |  |  |  |  |  |
Strike price (in dollars per share) | $ / shares |  |  |  | $ 18.74 |  |  |  |  |  |  |
Cap price (in dollars per share) | $ / shares |  |  |  | $ 22.95 |  |  |  |  |  |  |
Loss on derivative |  |  |  | $ 1,000,000.0 |  |  |  |  |  |  |
Convertible senior note [Member] | Senior notes [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Face amount |  |  | $ 86,300,000 |  |  |  |  |  |  |  |
Percentage of principal amount redeemed |  |  | 100.00% |  |  |  |  |  | 100.00% |  |
Proceeds from convertible notes |  |  | $ 83,700,000 |  |  |  |  |  |  |  |
Conversion ratio (in shares) |  |  | 53.3547 |  |  |  |  |  |  |  |
Conversion price (in dollars per share) | $ / shares |  |  | $ 18.74 |  |  |  |  |  |  |  |
Interest rate, cash percentage |  |  | 2.75% |  |  |  |  |  |  |  |
Threshold percentage of stock price trigger |  |  |  |  |  |  |  |  | 130.00% |  |
Threshold trading days |  |  |  |  |  |  |  |  | 20 days |  |
Consecutive trading days |  |  |  |  |  |  |  |  | 30 days |  |
Convertible senior note [Member] | Senior notes [Member] | Level 2 [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fair value of debt instrument |  |  |  |  |  |  | $ 83,500,000 |  | $ 83,500,000 |  |
Revolving credit facility [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate, percentage |  |  |  |  |  |  | 5.375% |  | 5.375% |  |
Revolving credit facility [Member] | U.S. revolving credit facility [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate, percentage |  |  |  |  |  |  | 3.75% |  | 3.75% |  |
Credit facility face amount |  |  |  |  |  |  | $ 175,000,000.0 |  | $ 175,000,000.0 |  |
Outstanding borrowings |  |  |  |  |  |  | 39,600,000 |  | 39,600,000 |  |
Credit facility maximum amount |  |  |  |  |  |  | 175,000,000.0 |  | 175,000,000.0 |  |
Revolving credit facility [Member] | U.S. letter of credit [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Letter of credit sub-facility amount |  |  |  |  |  |  | 110,000,000.0 |  | 110,000,000.0 |  |
Revolving credit facility [Member] | U.S. revolving credit facility, accordion [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Credit facility face amount |  |  |  |  |  |  | 50,000,000.0 |  | 50,000,000.0 |  |
Revolving credit facility [Member] | Iceland revolving line of credit [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Outstanding borrowings |  |  |  |  |  |  | 0 |  | 0 |  |
Credit facility maximum amount |  |  |  |  |  |  | 50,000,000.0 |  | 50,000,000.0 |  |
Revolving credit facility |  |  |  |  |  |  | $ 0 |  | $ 0 |  | $ 45,000,000.0
Hawesville [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Due to related parties, noncurrent |  |  |  |  | $ 40,000,000.0 |  |  |  |  |  |
Debt instrument, payment terms, number of monthly payments | payment |  |  |  |  | 24 |  |  |  |  |  |
London Interbank Offered Rate (LIBOR) [Member] | Hawesville [Member] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  |  |  | 5.375% |  |  |  |  |  |

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Exercise or strike price stated in the contract for options indexed to the issuer's equity shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 40 -Section 50 -Paragraph 5 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=123477628&loc=d3e90205-114008 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=109262807&loc=d3e22047-110879 + Details
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- Definition The cash inflow from the issuance of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585 + Details
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- Definition Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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